PROJECT SUMMARY Cutaneous leishmaniasis is endemic throughout the Amercias with an average 60,000 new cases reported annually. Colombia reports one of the highest numbers of cases in the region, second only to Brazil. The absence of a vaccine and the unsustainable vector control strategies translate into control measures based solely on case detection and treatment. The high frequency of therapeutic failure to first and second line antileishmanial drugs challenges these control measures. It is recognized that the outcome of antileishmanial treatment is multifactorial. However, the mechanisms that drive therapeutic cure or failure, and the host and parasite determinants of these divergent responses are only partially understood. In this project we will explore the participation of innate immune responses in the outcome of treatment of patients with cutaneous leishmaniasis caused by L. Viannia, and will seek to identify predictive and prognostic signatures of therapeutic responsiveness. To achieve this, we will characterize the magnitude, dynamics and regulation of innate inflammatory responses to explore complex non-linear interactions and to determine predictors of therapeutic outcome. This will be carried out by integrating access to affected populations with well characterized therapeutic responses, state-of-the-art transcriptomic profiling of primary innate cells and lesion biopsies from prospectively enrolled patients, functional characterization of TH17 responses in innate cell recruitment and activation, and statistical and machine learning analytics. We will challenge the dogma that parasite elimination is the central determinant of successful antileishmanial therapy and hypothesize that sustained recruitment and activation of innate immune cells to cutaneous lesions, driven respectively by pathogenic TH17 responses and TLR signaling and inflammasome activation, is a leading factor of treatment failure in CL patients. This will be achieved through the following aims: Aim 1) To determine the relationship of the innate immune response and inflammatory signaling to the clinical outcome of antileishmanial drug treatment Aim 2) To investigate the role of pathogenic and non-pathogenic TH17 subpopulations in activation and recruitment of innate cells to the lesion and in treatment outcome Aim 3) To construct classification and prediction models of therapeutic outcome. Understanding the role of innate immunity in the outcome of treatment will enable identification of host-specific predictive and prognostic signatures of the therapeutic response, and the rational selection of host-targeted therapeutics that redirect inflammation and revert pathogenicity.